Ultrasonic transducers are used as diagnostic devices for detecting tumors in the human body by the transmission and reception of ultrasonic waves.
Until now, ultrasonic transducers using piezoelectric vibration were used, but due to advances in the MEMS techniques in recent years, a capacitance detection type ultrasonic transducer (CMUT: Capacitive Micromachined Ultrasonic Transducer) wherein a vibrating part comprising a hollow part sandwiched between electrodes is mounted on a silicon substrate, is being intensively developed with a view to commercialization.
For example, U.S. Pat. No. 6,320,239 B1 (patent document 1) discloses a CMUT wherein a silicon substrate is used as the lower electrode.
U.S. Pat. No. 6,271,620 B1 (patent document 2) and 2003 IEEE ULTRASONICS SYMPOSIUM p. 577-p. 580 (non-patent document 1) disclose CMUT formed on lower electrodes which are patterned.
U.S. Pat. No. 6,571,445 B2 (patent document 3) and U.S. Pat. No. 6,562,650 B2 (patent document 4) disclose a technique wherein a CMUT is formed above a signal processing circuit formed on a silicon substrate.